Pollution Could Drain Earth's Water Cycle
Article courtesy the Environmental News Service
December 10, 2001
DIEGO, California, December 7, 2001 (ENS) - Pollution
produced by humans may be seriously weakening the Earth's
water cycle - reducing rainfall and threatening fresh
water supplies. A new study by researchers at the Scripps
Institution of Oceanography suggests that tiny particles
of soot and other pollutants are having a far greater
effect on the planet's hydrological cycle than previously
A United Nations Population Fund report released November
7 found that water use has grown six-fold over the past
70 years. "Water may be the resource that defines the limits
of sustainable development," that report noted.
But pollution may be slowly draining the water supplies
on which humans and other species depend, suggests the
study by Scripps researchers at the University of California,
San Diego. Tiny aerosols, primarily made up of black carbon,
can lead to a weaker hydrological cycle, which directly
affects fresh water availability and quality, the authors
The paper, based on results obtained during the international
Indian Ocean Experiment (INDOEX), appears in today's issue
of the journal "Science."
we were seeing aerosols as mainly a cooling agent, offsetting
global warming. In this article we are saying that perhaps
an even bigger impact of aerosols is on the water budget
of the planet," said Scripps professor V. Ramanathan,
who along with professor Paul Crutzen, a coauthor of the
new study, led the INDOEX science team as co-chief scientists.
"Through INDOEX we found that aerosols are cutting down
sunlight going into the ocean," added Ramanathan. "The energy
for the hydrological cycle comes from sunlight. As sunlight
heats the ocean, water escapes into the atmosphere and falls
out as rain. So as aerosols cut down sunlight by large amounts,
they may be spinning down the hydrological cycle of the
The fourth co-author of the paper, Daniel Rosenfeld, also
notes that these aerosol particulates may be suppressing
rain over polluted regions. Within clouds, aerosols can
limit the size of cloud droplets, stifling the development
of the larger droplets required for raindrops.
If pollutants cut back on rain and snowfall, it could
directly affect the replenishment of the world's major
stores of freshwater, including lakes, groundwater supplies,
glaciers and high elevation snowpack. If humans continue
to draw down these stores at a faster rate than they are
replenished, access to fresh water could become the most
crucial problem facing civilization.
The INDOEX project involved more than 150 scientists across
several disciplines from Austria, France, Germany, India,
Maldives, the Netherlands, Sweden and the United States.
The $25 million project, funded in part by the National
Aeronautics and Space Administration (NASA), focused on
the Indian Ocean region in a multiplatform analysis using
satellites, aircraft, ships, surface stations and balloons.
The project was designed to assess the nature and magnitude
of the chemical pollution over the tropical Indian Ocean
and to evaluate the environmental significance of the
Early in the project, INDOEX researchers documented a human
produced brownish gray haze layer of about 10 million square
kilometers over the Indian-Asian region. The particles within
the haze, the researchers discovered, were causing a three-fold
decrease in solar radiation reaching the earth's surface
as compared with the top of the atmosphere.
The aerosols, typically in the submicrometer- to micrometer-size
range, were a mixture of sulfates, nitrates, organic particles,
fly ash, and mineral dust, formed by fossil fuel combustion
and burning of forests and other biomass.
of the key revelations from INDOEX is that air pollution
is not only an industrial phenomenon," said Scripps professor
Crutzen, a 1995 Nobel Laureate. "The part of the atmosphere
that you would expect to be the cleanest - the areas without
a lot of industrialization - in fact can be very highly
polluted, especially during the dry season."
In the new "Science" article, Ramanathan, Crutzen, J.T.
Kiehl of the National Center for Atmospheric Research,
and Rosenfeld of the Hebrew University of Jerusalem, say
the aerosol issues raised by INDOEX are a "major environmental
The team not only questions the role aerosols are playing
on the regional and global water cycle, but they also suggest
that aerosol pollution increases the solar heating of the
atmosphere, and reduces the solar heating of the surface
of the planet. These effects maybe comparable to the global
warming effects of greenhouse gases, the team argues.
present these effects are not generally accounted for
in climate model prediction studies, but we will need
to include the absorbing aerosols in future model predictions,"
The immediate next step, the authors say, is to develop
a reliable global inventory of aerosol emission rates,
life times and concentrations. Integrating new satellite
observations, field experiments and laboratory studies
with computer models will pave the way for breakthroughs
in scientific understanding of aerosols and how they are
modifying the environment, they say.
"Part of these results are important for creating awareness,"
said Crutzen. "The biomass burning in the countries that
are producing this pollution cannot go on."
The "Science" study was funded by the U.S. Department
of Energy, the National Oceanic and Atmospheric Administration
(NOAA), NASA and the National Science Foundation.